Process for producing the electric insulation of electric machine windings

ABSTRACT

In order to produce the electric insulation of the winding of an electric machine, grooves having a cross-section that tapers at least in an area near to the groove opening are arranged in the rotor or motor. Before the winding is laid in the grooves, the latter are lined with a laminate that contains an elastically compressed mass of high-elastic, electrically insulating fibres and a solidified, curable synthetic resin that can still be thermally softened, however, and that holds the mass of fibres in its compressed state. Once the winding is laid and the grooves are closed, the rotor or stator is subjected to a vacuum pressure impregnation, then cured. During the impregnation process, the hot saturating resin penetrates into the pores of the elastically expandable laminate, elastically expanding the mass of fibres and filling the empty spaces in the grooves, so that the elastically expanded mass of fibres, that is supported at the surface of the groove, exerts on the upper subconductor bundle of the winding a force in the direction of the bottom of the grooves.

TECHNICAL DOMAIN

The invention relates to a process for manufacturing the electricalinsulation of the winding of an electrical machine which has windingsections, particularly subconductor bundles, which are placed with playin the grooves of the rotor or stator.

STATE OF THE ART

The quality of the electrical insulation of the windings of electricalmachines, i.e., motors and generators, can be impaired to a considerabledegree by the occurrence of air gaps between the individual layers ofthe insulating, and in particular, by air gaps between the outerinsulating layers of the winding and the inner walls of the grooves inthe laminate housing of the rotor or stator of the machine in which thewinding is placed. Such air gaps have a detrimental effect on thedischarge of the Joule heat occurring in the winding during operationinto the laminate housing.

Air inclusions and air gaps inside the insulation itself can be largelyprevented by other known technologies. However, this applies only to alimited degree to the prevention of air gaps between the outermost layerof the insulation and the inner walls of the groove. For manufacturingreasons, it is generally not possible to make both side walls of thegroove in the laminate housing fully uniform and plane-parallel. Even ifa subconductor bundle to be placed in the groove had a perfectedprismatic cross-section, it would only be possible to place it in thegroove with a more or less large degree of play between the surface ofthe insulated subconductor bundle and the two side walls of the groove.

According to the so-called "resin-rich" process for the manufacture ofinsulation of windings of electrical machines, a technique is known inwhich the insulation is composed of insulating materials which have sucha high content of binders in the form of thermosetting synthetic resinthat because the synthetic resin becomes fluid during manufacturing, airinclusions can be avoided. In this process, following the application ofthe insulating materials, the winding is heat-treated in an expansivedevice and brought into a pressing process involving hardening of thesynthetic resins contained in the insulation down to a preciselypredetermined size, which makes it possible to achieve a relatively lowdegree of play between the winding and the inner walls of the groove.

According to another process, referred to as the vacuum pressureimpregnation process, the insulation of the winding consists at least toa large extent of absorbent, porous insulating materials. Afterplacement of the winding in the grooves, however, there is initially alarger play between the winding and the inner walls of the groove. Therotor or stator having the winding is then impregnated with athermosetting impregnating resin in a vessel. In this process, in aninitial step, the rotor or stator is placed under a vacuum in theimpregnation vessel, which removes the air from the pores and/or gaps,after which it is placed in the impregnation resin bath. The subsequentproduction of excessive pressure in the impregnation vessel makespenetration of the impregnation resin into the pores and gaps easier. Insubsequent heat treatment under elevated temperature, the impregnationresin absorbed by the rotor or stator and the binders and syntheticresins in the insulation are hardened.

However, experience shows that in the case of conventional vacuumpressure impregnation processes as well, the occurrence of air gapsbetween the subconductor insulation and the inner walls of the groovecannot be reliably prevented.

In order to remedy this, the applicant of the older international patentapplication, PCT/AT91/00021, suggested that, for the manufacture of theelectrical insulation of the winding of an electrical machine accordingto the vacuum pressure impregnation process, the grooves be fitted witha laminate prior to laying the winding into the grooves of the stator orrotor, which laminate would contain at least one laminate layer made ofan elastically compressed, highly elastic, electrically insulated fibermaterial and a solidified, curable synthetic resin, which can, however,be thermally softened and which holds fiber material in its compressedstate. Once the winding is laid and the grooves are closed, the rotor orstator is subjected to vacuum pressure impregnation and subsequentlyhardened in an oven. During the impregnation process, the hotimpregnating resin also penetrates the pores of the elasticallyexpandable laminate in particular. This causes the synthetic resin tomelt, in turn causing the fiber material to expand elastically, thusevenly filling the gaps in the groove so that air inclusions in thegroove are reliably prevented.

DESCRIPTION OF THE INVENTION

The purpose of the Invention is to alter the process of manufacturingthe insulation of the winding of an electrical machine as described inthe cited international patent application in such a way that bettermechanical fixation of the windings in the grooves is obtained.

The purpose of the Invention is achieved by the process according to theinvention, which is characterized in that grooves are provided whosecross-section, at least in the area of the groove depth in which thegroove opening is approached, tapers in a radial direction towards thegroove opening and that--at least in this area--a laminate which expandsunder heating is inserted into the gap-shaped space which forms betweenthe groove surface and the winding sections or subconductor bundles,this laminate containing an elastically compressible, highly elasticfiber material as well as a solidified, curable synthetic resin, whichcan, however, be thermally softened and which maintains the fibermaterial in its compressed state, and that the laminate is then heatedin order to soften the synthetic resin, whereupon the laminate expandsbecause of the released tension on the compressed fibers and fills outthe aforementioned gap-shaped space in such a manner that, in the citedarea of the tapering groove cross-section, the remaining mechanicalcompression causes the elastically expanding fiber material, supportingitself on the groove surface, to exert at least on an inserted windingsection or a subconductor bundle a considerable component of force inthe direction of the bottom of the groove, and that the synthetic resinis subsequently hardened at an increased temperature. In this process,the heating of the synthetic resin is preferably performed byimpregnating the laminate with a hot, liquid, thermosetting material asan impregnating medium, which fills the pores of the expanded laminate.

According to advantageous modes of implementation of the process of theinvention, the groove opening is closed by a temporary or permanent nibfixture prior to the expansion of the fiber material in the laminateused. In this case, a winding made from a temperature-contracting tapewhich is removably attached to the rotor surface can be used as a nibfixture to temporarily close the groove openings of a rotor, or apreferably removable, divisible, cylindrical template can be used as anib fixture to temporarily close the groove openings of a stator. Inadvantageous modes of implementation of the process of the invention,breech wedges or backplates which are secured in lateral mountinggrooves designed into the side walls of the groove can be used aspermanent nib fixtures to close the groove openings.

In a further advantageous mode of implementation of the process of theinvention, the area in which the groove cross-section tapers towards thegroove opening is at or near the groove opening, with its depth beingless than half of the groove depth and the upper edge of the windingsection or subconductor bundle which is laid in the groove and isclosest to the groove opening lying within this area.

In further advantageous modes of implementation of the process of theinvention, the laminate used has a film of electrically insulatingmaterial on one or both sides which border the elastically expandinglayer, with the laminate being laid into the gap-shaped space with thefilm side facing the groove wall or the laminate laid in having a filmof electrically insulating material on both sides. In the laminate used,at least one of the films can advantageously consist of polyester orpolyimide, while the elastically expandable layer of the fiber materialshould preferably consist of glass fibers, aramide fibers or polyesterfibers.

In another advantageous mode of implementation of the invention, thefiber material in the elastically expandable layer of the laminate ismanufactured on the basis of fiber fleece, glass fiber mats, or fiberfelts. In a final advantageous mode of implementation of the process ofthe invention, the elastically expandable layer of the laminate has asynthetic resin content of 10 to 40% by weight, and preferably asynthetic resin content of 10 to 28% by weight.

Several Modes of Implementation of the Invention Explained by Means ofFigures

In implementing the process according to the invention, a laminate isrequired which is manufactured in the following manner according to anexample of the process.

A strip of glass fiber fleece with a specific weight of 60 g/m² and athickness of 1.0 mm manufactured from cut, non-oriented, alkaline-freeglass filaments is impregnated with a resin which consists of 98.4% ofan epoxy resin based on a diglycidyl ether of bisphenol A and of 1.6% ofzinc naphthenate in such a way that the resin content of the impregnatedstrip of glass fiber fleece is 20% by weight. The addition of the zincnaphthenate has the advantageous effect on the remainder of the processof lowering the Kofler melting range of the epoxy resin used, whichwould otherwise be approximately 120° C., so that the impregnation resinitself has a melting range of about 70° C.

Impregnation takes place in an impregnation apparatus in which thecontinuously fed-in strip of glass fiber fleece is subjected to drippingof a solution of the impregnating resin in methylethylketone as asolvent, and the solution is then evaporated while passing through adrying duct. The strip of glass fiber fleece impregnated in this manneris then cut into pieces of defined length and stacked in the usualmanner.

As schematically shown in FIG. 1, in order to manufacture the laminate,the impregnated glass fiber fleece 1 is placed on the press metalsupport 2 and covered with a polyester film 3 (polyethyleneterephthalate) with a thickness of 0.03 mm. This stack, which has athickness of 1.05 mm, is then moved on the press metal support into apress with press plates which can be heated and recooled and iscompressed to a thickness of 0.45 mm by moving the press plates againstspacer strips. The press plates are then heated to 120° C., and thistemperature is maintained for approximately 1 hour. In this process, thepressed material is thoroughly heated, and the impregnating resin issoftened due to its low melting range, after which it becomes fluid andis uniformly spread through the volume of the fiber mat. After this, thepress plates and the pressed material are cooled down to roomtemperature, which causes the impregnating resin to solidify again, andthe compressed stack 4 is converted into the finished laminate 5--seeFIG. 2--which is then discharged from the press.

The manufacturing of the electrical insulating of the winding of anelectrical machine and its placement in the groove will now be explainedby means of FIG. 3.

FIG. 3 shows a section through a groove 6 in the laminate housing 7 ofthe rotor together with the two subconductor bundles 8 shown assections. Each of the subconductor bundles 8 consists of ten copperconductors 9, whose single-conductor insulation can consist of amica/plastic film compound which has a relatively high binders contentand subconductor bundle insulation having a low binder content, such asmica/glass fibers not shown in the Figure.

The cross-section of the groove 6 exhibits a special shape: starting atthe bottom 10 of the groove, the groove cross-section initially expands,after which it again tapers within an area 12 lying next to grooveopening 11. Within this area 12, the laterally even sections 13 of thegroove surface are each directed inwards at an angle which canadvantageously be between 4° and 6°.

A precut and prefolded shell 14 of the described laminate, having thesame width as the bottom 10 of the groove, is first placed in each ofthe still-empty grooves 6, with the cover areas 13 of the shell 14,shown lying above one another in FIG. 3, still unfolded. The expandablelaminate 5 of shell 14 is oriented so that its film side faces thegroove wall. The winding is then laid in the groove 6, with a strip 16of the expandable laminate 5 being placed between each of the twosubconductor bundles 8 as well as over the upper subconductor bundle.Finally, the two cover areas 15 of the shell 14 are folded over eachother and secured by gluing. After the winding has been laid in thegrooves as described above, a winding 17 made of atemperature-contracting tape is placed on the rotor surface. FIG. 3shows the arrangement in this phase of the process.

The rotor is then subjected to conventional vacuum pressure impregnationand subsequently hardened at an increased temperature in an oven.

In the impregnating process, the hot and relatively fluid impregnatingresin penetrates all free gaps and pores within the groove and thewinding insulating, particularly the pores of the expandable laminatematerial of the shell 14 and the strip 16. This causes the resin whichmaintains the fiber material in a compressed state to melt, causing thefiber material to be elastically decontracted, thus filling out thegap-shaped space in the groove and the cavity between the winding17--which forms a temporary nib fixture--and the upper surface side ofthe upper subconductor bundle 8 respectively. After the rotor has beenhardened in the oven, the winding 17 is removed, and one obtains aconfiguration like the one shown in the diagram in FIG. 4.

Because of the remaining mechanical compression, the elasticallyexpanding fiber material which supports itself against the sections 13of the groove surface exerts a considerable force on the uppermost ofthe two subconductor bundles 3 in the area 12 of the tapering groovecross-section, in the direction shown by the arrow 18, i.e., in thedirection of the bottom 10 of the groove. This causes the twosubconductor bundles 8 to be maintained under tension in the groove 6,which leads to a significant increase in the stability of the fixationof the winding in the grooves.

In contrast to the variants of the process of the invention describedwith reference to FIGS. 3 and 4, where one makes do with a temporary nibfixture in the shape of the winding 17, permanent nib fixtures are usedin the process variant of the FIGS. 5 and 6 and of FIG. 7 respectively.

FIG. 5 shows a groove 19 whose cross-section is shaped similarly to thegroove 6 of FIG. 3, but in which the tapering cross-section in the area12 does not reach the groove opening 11; rather, an area 20 withplane-parallel side walls of the groove adjoins it in which mountinggrooves lying opposite one another have been designed, which hold abackplate 21. For the remainder, the arrangement of the two subconductorbundles 8 of the shell 14 and the laminate strips 16 is identical tothat shown in FIG. 3. FIG. 6 shows the configuration of the arrangementof FIG. 5 after expansion of the elastically compressed fiber material.

FIG. 7 represents a groove 22 with inserted winding which is identicalto the one of FIG. 5, with the difference that a breech lock 23 isattached in place of a backplate.

FIGS. 8 and 9 demonstrate the manufacture of the electrical insulationof the stator of an electrical machine as well as its fixation in thegrooves 24.

In FIG. 8, the cross-section of a groove 24 in the stator laminatehousing 25 with two diagrammatically outlined subconductor bundles 26 isshown. The groove 24 has groove side surfaces 27 which are laterallylevel and which are directed inwards at an angle of 1.5° each. The twosubconductor bundles 26 each have five conductors 28. The arrangement ofthe shell 14 and the strips 16 is similar to that of the rotor variantof FIGS. 3 and 4. A removable and divisible template, which is indicatedon 29 in FIG. 8 and covers all grooves of the stator, serves as atemporary nib fixture. The expansion of the elastically compressed fibermaterial during vacuum pressure impregnation causes a force to beapplied primarily to the subconductor bundle lying at the groove openingand shown by the direction of the arrow 30 (see FIG. 9). After thestator has been hardened in the oven, the template 29 is removed, andone obtains the configuration shown in FIG. 9.

The arrangement of the laminate in the gap between the groove wall andsubconductor surface with the film facing the groove wall has theadvantage that, when the winding is disassembled, it acts as a so-calledseparation film.

The laminate used in the process may consist of various layercombinations. In the case of a 2-layer construction, which consists of afilm and an elastically expandable layer, for example, a polyester filmis used for machines of class F and a polyimide film, or a filmcombination containing a polyimide film, for machines of class H. Theelastically expandable layer should preferably be manufactured fromglass fiber fleece, a glass fiber mat, a polyester felt, or an aramidefelt (Nomex felt).

Commercial Applicability

The process according to the invention can be particularly advantageousin the manufacture of traction engines and in all machines in which thegrooves in the laminate housing of the rotor or stator have a groovecoating.

We claim:
 1. A process for manufacturing the electrical insulation ofthe winding of an electric machine, said machine having a rotor and astator, each of which having radially directed grooves with grooveopenings, which has winding sections or subconductor bundles placed withplay in the grooves of the rotor or stator comprising providing grooveswhose cross-section proximate to the groove opening, tapers in a radialdirection inwardly towards the groove opening, inserting at least in thearea proximate to the groove opening, a laminate which expands underheating into the gap-shaped space which forms between the groove surfaceand the winding sections, this laminate containing an elasticallycompressible, highly elastic fiber material as well as a solidified,curable synthetic resin, which can, however, be thermally softened andwhich maintains the fiber material in its compressed state, heating thelaminate in order to soften the synthetic resin, whereupon the laminateexpands because of the released tension on the compressed fibers andfills out the aforementioned gap-shaped space such that, in said area ofthe tapering groove cross-section, the elastically expanding fibermaterial exerts at least on an inserted winding section or asubconductor bundle a considerable component of force in the directionof the bottom of the groove, and hardening the synthetic resin at anincreased temperature.
 2. The process of claim 1, wherein heating of thesynthetic resin takes place via impregnation of the laminate with a hotliquid thermosetting material as an impregnation medium, which fills upthe pores of the expanded laminate.
 3. The process of claim 1, whereinprior to the expansion of the fiber material in the laminate used, thegroove opening is closed by a temporary or permanent nib fixture.
 4. Theprocess of claim 3, further comprising applying a removable winding madeof a temperature-contracting tape to the rotor surface to temporarilyclose the groove openings of the rotor.
 5. The process of claim 2,wherein a removable, divisible, cylindrical template serves as a nibfixture to temporarily close the groove openings of a stator.
 6. Theprocess of claim 2, further comprising providing breech locks orbackplates which are held in lateral mounting grooves in the side wallsof the groove as permanent nib fixtures to close the groove openings. 7.The process of claim 1, wherein the area in which the groovecross-section tapers towards the groove opening or lies near the grooveopening has a depth which is less than half the groove depth and thatthe upper edge of the winding section or subconductor bundle lyingclosest to the groove opening and facing the groove opening is locatedwithin this area.
 8. The process of claim 1, wherein the laminate has afilm of electrically insulating material on at least one side which isadjacent to the elastically expanding layer.
 9. The process of claim 8,further comprising placing the laminate with the film side facing thegroove wall in the gap-shaped space.
 10. The process of claim 8, whereinthe laminate has a film of electrically insulating material on bothsides adjacent to the elastically expandable layer.
 11. The process ofclaim 1, wherein the laminate has a film of electrically insulatingmaterial on both sides adjacent to the electrically expandable layers.12. The process of claim 8, wherein the laminate contains at least onefilm consisting of polyester.
 13. The process of claim 8, wherein thelaminate contains at least one film consisting of polyimide or containspolyimide in a film compound.
 14. The process of claim 1, wherein thefiber substance in the elastically expandable layer of the laminateconsists at least predominantly of glass fibers.
 15. The process ofclaim 1, wherein the fiber substance in the elastically expandable layerof the laminate consists at least predominantly of aramide fibers. 16.The process of claim 1, wherein the fiber substance in the elasticallyexpandable layer of the laminate consists at least predominantly ofpolyester fibers.
 17. The process of claim 1, wherein in the elasticallyexpandable layer of the laminate, the fiber material is manufactured offiber fleece, fiber mats, or fiber felts.
 18. The process of claim 1,wherein the elastically expandable layer of the laminate has a syntheticresin content of 10 to 40% by weight.
 19. Process of claim 18, whereinthe elastically expandable layer of the laminate has a synthetic resincontent of 10 to 28% by weight.